Testing apparatus



Nov. 29, 1955 c. M. RIVELY ETAL 2,725,525

TESTING APPARATUS Filed March 13, 1951 INVENTORS C. M. Ell/El) IV. E. GLE/M ATTORNEY TESTING APPARATUS Application March 13, 1951, Serial'No. 215,336

6 Claims. Cl. 324-33 Our invention relates to testing apparatus and, more pariiicularly, to apparatus for testing gas-filled lamps for ca s.

Photofiash lamps are exhausted and filled with a gas such as oxygen to eifect combustion of the primer. The gas pressure within the lamp is below atmospheric and therefore the gas inside will become contaminated with atmospheric air if there are any leaks in the envelope. Photoflash lamps are tested for leaks in the envelope by establishing a glow discharge in the lamp and determining from the color of the discharge whether or not any atmospheric gas has leaked into the bulb.

In the past an electrode at high potential has been held near the outside surface of the envelope and a glow discharge has been struck between the electrode and an antenna wire in the lamp which was connected to ground through one terminal of the lamp. The antenna wire was necessary to prevent the primer in the lamp from being flashed by a discharge between the outside electrode and the filament, or the filament support and leadin connection. In designing testing apparatus and methods for testing lamps, the prevention of flashing of the primer is always a prime consideration.

The principal object of our invention, generally considered, is to devise a simple and improved method-of testing photoflash lamps.

Another object of our invention is to test photoflash lamps with a glow discharge without requiring the use of an antenna wire within the lamp to prevent flashing of the primer.

Yet another object of our invention is to design circuits and apparatus for applying a high ionizing potential to photoflash lamps without flashing the primer.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself, however, together with additional objects and advantages thereof, may be best understood from the following description of a specific embodiment when read in conjunction with the accompanying drawing in which the sole figure is a schematic showing of the electrical circuit used in practicing our invention.

There is shown in the drawing an ordinary photoflash lamp 1 which has a glass envelope 2 and a cup-shaped base 3 sealed to the glass envelope. As is customary, the outside cylindrical periphery of the base 3 serves as one outside terminal 4 for the lamp; the other outside connection is made to a second terminal 5 which is located on the bottom of the cup-shaped base 3 and is insulated from the sides of the cup.

Running from the terminals 4 and 5 into the glass envelope are lead-in wires 6 and 7 which also act as filament supports. A filament 8 is fastened near the ends of the lead-in wires 6 and 7 and the primer material 9 is applied to the junction of the filament and the lead-in wires. It is this priming material which we must be careful not to flash during testing. Before sealing and basing the lamp, a small dot of conducting material 10,

nited States Patent-0 2,725,525 Patented Nov. 29, 1955 2 such as aluminum or graphite, is desirably, but not necessarily, placed on the inside of the envelope 2 directly opposite the part of the envelope where the base 3 is to be sealed. The envelope is also filled with a gas, preferably oxygen, to effect combustion of the primer.

In order to provide the necessary R.-F. potential for causing a glow discharge in the gas of the lamp, we use a circuit which is in effect two Tesla coils connected in series. Transformer 22 is connected to an ordinary or commercial source of potential, the secondary winding 24 of the transformer being shunted by spark gap 26. Condensers 28 and 30 are connected in series with the secondary 24. Between the two condensers 28v and 30, and connected in series therewith, are two series-connected coils 32 and 34. Coil 32 and coil 34 are primary windings of transformer 38 and transformer 40, respectively, which have as their secondary windings, respectively, coil 42 and coil 44. 1

The low end of each of the secondary coils 42 and 44 is eflectively grounded through condensers 28 and 30 and spark gap 26 as far as R.-F. current is concerned, while the other end of each coil is connected to an electrode. For example, secondary coil 42 may be connected to electrode 46 and secondary coil 44 may be connected to electrode 48.

The current flow through the primary coil 32 of transformer 38 is opposite the current flow through the primary coil 34 of transformer 40. Consequently, when oneelectrode is at a potential positive with respect to ground, the other electrode is at an equal but negative potential with respect to ground since the current flow through the secondaries 42 and 44 is also in opposite directions. A current surge through the primaries of transformers 38 and 40 is produced when the potential across the spark gap 26 builds up to a high enough value to cause a discharge across the; gap. This causes the condensers 28 and 30 to discharge themselves through the primary coils 32 and 34 of transformers 38 and 40, thereby creating a current surge in the primaries resulting in a high potential at electrodes 46 and 43. .In practice, the primaries of transformers 38 and 40 desirably have three turns and the secondaries 110 turns.

To test a lamp, the envelope is placed between the electrodes 46 and 48, each electrode being approximately an equal distance from the metal dot 10 and so positioned that the dot lies in the straight line joining the two electrodes. The distance between the electrodes 46 and 48 should be less than the distance from the electrodes to the filament 8 which is at ground potential. The spacing limits of the electrodes are determined by the breakdown characteristics between the electrodes and between the electrodes and the filament. -Since the distance between electrodes 46 and 48 is less in the embodiment shown in the drawing than the distance from the electrodes to the filament 8, and since the potential diiference between electrode 46 and electrode 48 is twice as great, one electrode being x volts above ground and the other x volts below ground, as the potential difi'erence between either electrode and the filament, which is grounded as indicated at 49, any glow discharge will tend to take place between the two electrodes 46 and 48.

Therefore, by applying a potential substantially above the lamp potential to one electrode and a potential substantially below lamp potential to the other electrode the danger of flashing the primer by causing a glow discharge between either electrode and the filament is eliminated. The small metal dot 10 aids in striking the discharge between the electrodes 46 and 43, thus insuring that the discharge will take place between the electrodes 46 and 48 and not between the electrodes and the filament 8. Once the discharge takes place, the operator can tell by the color whether or not any impurities have leaked into the gas-filled envelope.

Thus it can be seen from the foregoing that we have provided an improved method ofand apparatus for testing photoflash lamps by using a glow discharge, which method is simple and does not require the use of an antenna wire within the lamp.

Although a preferred embodiment of our invention has been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

We claim:

1. Apparatus for testing gas-filled lamps having primer material on the filament thereof comprising, an electrode, a second electrode spaced from said electrode, said electrodes being adapted to receive a lamp between them, the distance between electrodes being lass than the distance from either electrode to the filament of said lamp, a means for applying a potential to each of said electrodes to cause a glow discharge in the lamp, the potential of each electrode being equal but of opposite polarity with respect to ground.

2. Apparatus for testing gas-filled lamps having primer material on the filament thereof comprising, an electrode, a. second electrode spaced from the first electrode, said electrodes being adapted to receive a lamp therebetween, the distance between the said electrodes being less than the distance from either electrode to the filament of lamp being tested, a dot of conducting material between the electrodes supported by and on the inside of the lamp being tested, a means for applying a potential to each of said electrodes to cause a glow discharge within the lamp being tested, the potential of each electrode being equal but of opposite polarity with respect to ground.

3. Apparatus for testing a gas-filled envelope comprising two spaced electrodes adapted to receive said envelope therebetween, and means to apply to one of said electrodes a potential substantially above the potential of said envelope and to the other of said electrodes a potential substantially below the potential of said envelope thereby causing within said envelope an ionization of the gas between said electrodes.

4. An arrangement for testing a gas-filled envelope comprising two spaced electrodes adapted to receive said envelope therebetween, a dot of conducting material between said electrodes and supported by the inside surface of said envelope, and means" for applying a potential substantially above the potential of said envelope to one of said electrodes and a potential substantially below that of said envelope to the otherof said electrodes thereby causing within said envelope an ionization of the gas between said electrodes.

5. An apparatus for testing gas-filled lamps having primer material on the filament thereof comprising an electrode, a second electrode spaced from said electrode, said electrodes being adapted to receive a lamp envelope between them, said lamp envelope obstructing the straight line path between said electrodes, the distance between said electrodes being less than the distance from either electrode to the filament of the lamp being tested, said filament being at a reference potential, a means for applying a potential to each of said electrodes to cause a glow discharge between said electrodes within the lamp being tested, the potential of each electrode being equal but of opposite polarity with respect to said reference potential.

6. An apparatus for testing gas-filled lamps having primer-material on the filament thereof comprising an electrode, a second electrode spaced from said electrode, said electrodes being adapted to receive a lamp envelope between them, said lamp envelope obstructing the straight line path between said electrodes, the distance between said electrodes being less than the distance from either electrode to the filament of the lamp being tested, said filament being at ground potential, a means for applying a potential to each of said electrodes to cause a glow discharge between said electrodes within the lamp being tested, the potential of each electrode being equal but of opposite polarity with respect to ground.

References Cited in the file of this patent UNITED STATES PATENTS 1,917,465 Schweitzer July 11, 1933 2,370,475 Lemmers Feb. 27, 1945 2,590,778 Lautenberger Mar. 25, 1952 2,633,486 Sweet Mar. 31, 1953 

